There are two ways of protecting animals against infectious agents: they can be exposed to antigens derived from an infectious agent to stimulate a protective immune reaction or they can receive a preformed antibody obtained from an immunized subject.
The first way is conducted through different types of vaccines: freeze-dried live viruses or bacteria, through dead viruses or bacteria in oily emulsions; and recently through the creation of cloned and recombinant vaccines. Each of them presents advantages and drawbacks with regard to protection, immune response and protection duration. Besides, in some cases, the first general approach may lead to undesirable complications in the host due to the vaccination (Tizard, I. R. 1998)
The second form of protection, also called passive immunity, includes the transference of specific antibodies against infectious agents into A susceptible subject.
Traditionally, at the research level, antibodies are mainly obtained from mammals and less frequently from birds. The types of antibodies obtained are monoclonal and polyclonal antibodies in mammals, and polyclonal antibodies in birds (Larsson, et al. 1993).
In the case of birds, the chicken is the only species from which antibodies are obtained in a most accessible and highly defined form. The main serum antibody present in the chicken is IgG, even though IgG is transported to the egg in a similar way to the transfer of mammal IgG through the placenta.
In the egg, IgG is found in higher concentrations in the yolk than in the white; it is even found in larger quantities in the yolk than in the hen serum (Larsson, et al. 1993).
To have an idea of the quantity of antibodies made in the hen, we must take into account that an egg-laying hen produces approximately 5 to 6 eggs per week with a yolk volume of about 15 ml. Thus, in a week, a hen produces antibodies in yolk equivalent to 90-100 ml of serum or 180-200 ml of whole blood. This is to be compared with the 20 ml of whole blood given per week by an immunized rabbit. Obviously if we use animals such as horses or cows, the quantity of serum and antibodies is larger than in the egg but it is more expensive and more painful for the animals.
Egg yolk antibodies (immunoglobulins-Ig's) have been employed as tools for diagnosis and therapy (Schmidt, et al. 1989). Thus, taking advantage of its phylogenetic difference with mammal immunoglobulins, the Ig's have presented several advantages when used in immune diagnosis. For example, yolk Ig's have been used to detect several viruses through ELISA, immunodiffusion, and immunofluorescence. Because of their low isoelectric point, compared to human IgG, they are employed in electrophoresis assays for the quantification of immunoglobulins in the serum of several animals (Altschuh, D. 1984, Larsson, et g. 1988, Larsson, et al. 1992, Larsson, et al. 1993, Schade, R. 1996). With regard to their therapeutic application, the Ig's have been used as immunotherapy in some scientific fields. For example, the administration of egg yolk immunoglobulins orally has prevented rotavirus infections in mice, bovines, and pigs, among others (Ikemori, et al 1992, Kuroki, et al 1994, Marquardt, et al 1998). Moreover, they have been used as antivenins against viper and scorpions that can be injected to neutralize the toxins without the risk of anaphylactic reactions, such as those reactions commonly caused by antivenins obtained from immunized horses (Larsson, et al. 1993). A further application was to prevent caries caused by Streptococcus mutans in humans (Hata, H. et al 1984).
In the past, several methods have been used in attempts to control coccidiosis including the use of chemical drugs and vaccines including live and recombinant vaccines. However, there are problems with existing coccidiosis vaccines, such as reduced efficacy, cross-infection with other parasites (e.g., Clostridium sp.) and poor bird performance. Monoclonal and recombinant antibodies are still under experimentation. Vaccines would have some positive impact in preventing infections but they are not suitable for reducing ongoing infections.
At present the use of antibodies obtained from either mammals or birds for treatment or prevention of coccidia infections caused by Eimeria species has not been reported. Reynolds, in U.S. Pat. No. 5,807,551, describes a method for inducing long-term passive immunity in birds but research was limited to Newcastle disease virus and infectious bursal disease virus. Sterling et al., in U.S. Pat. No. 5,753,228, discloses a method for treating infestions caused by Cryptosporidium parvum in mammals. Thus, there is a need for efficacious coccidiosis and coccidiosis control methods.